Abstract: This paper presents a simplification method of Petri net based on knowledge reduction.With the method of attribute-oriented reduction，it removes the redundancy rules and conditions of production rules corresponding to Petri net，and then simplifies the rules to the key rules.The paper also transforms the simplified production rules into Petri net model in which the number of nodes is reduced and the net system is simplified in certain degree.The simplified model contains the same information as before，but the numbers of place and transition are reduced.The reasoning process based on the model becomes easier and more efficient.Using a disease case to test the method at the last，the results show that this method is simple and practical，the complexity of time and space is efficiently reduced far and away，and the efficiency of searching and reasoning is improved.